The term "ultrasonic radiation" is employed in this specification to designate pressure-rarefaction waves differing from sound waves in exhibiting higher frequencies and shorter wavelengths. The term "ultrasonic exposure" is employed to designate exposure to ultrasonic radiation. The production of visible images by means of ultrasonic radiation is referred to as "ultrasonoscopy". The production of a visible record by means of ultrasonic radiation is referred to as "ultrasonography". The instruments for producing ultrasonoscopic images are designated "ultrasonoscopes", and the ultrasonoscopes which produce ultrasonographic images are referred to as "sonographic cameras". The definition of terms as here presented is believed to be generally consistent with the use of these terms in the art. Specifically, these terms are suggested by P. J. Ernst in the Journal of the Accoustical Society of America, Vol. 22, No. 1, in an article entitled "Ultrasonography", pp. 80-83, January 1951.
The prior state of the art with respect to the action of ultrasound on silver halide photographic elements is reviewed by M. E. Arkhangel'skii, Soviet Physics--Acoustics, Vol. 12, No. 3, "Action of Ultrasound on the Processes of Photographic Development and Fixing", pp. 241-248, January-March 1967. The ability of ultrasound exposure to produce a latent image in silver halide emulsions has been recognized since the 1930's. However, power level requirements to achieve ultrasonic imaging have been quite high, and there have been controversies as to whether the ultrasound directly produces the latent image or stimulates other effects, such as cavitation-stimulated luminesence, which produces the latent image. It has been recognized that higher maximum densities are attainable for a given power level of ultrasonic exposure when the photographic element is in contact with a photographic developer. Arkhangel'skii observed that if the photographic element is first light exposed and then ultrasonically exposed in a developer, the ultrasonic time and intensity to produce a density obtainable in the absence of light exposure decrease to a few minutes and a few watts per square centimeter, respectively.
It has been a difficulty in the art that ultrasonic exposure requirements of silver halide photographic elements, even with the most responsive techniques known, have remained unattractively high. For example, such techniques have required intensity and time levels of ultrasonic exposure which are objectionable to many nondestructive testing applications, such as mammographic examination with ultrasound as described by Brendon U.S. Pat. No. 3,765,403. A further disadvantage has been that ultrasonic effects on the developability of silver halide have not been noted to provide good resolution, to the extent that many investigations have merely reported effects, but provided no indication that imaging was obtained or obtainable. Further, known processes which require ultrasound exposure of light fogged silver halide elements in the course of development are inherently prone to poor resolution and development in background areas--e.g., elevated minimum densities.